Project Summary/Abstract Trauma is the leading cause of death and disability among young adults in the United States. Trauma affects all segments of the US population, but large disparities exist in access to high quality trauma care and outcomes after injury. Among young adults, uninsured patients, patients who reside in low income communities, and black patients have higher risk-adjusted rates of in-hospital mortality. Low income and black and Hispanic patients are also less likely to receive rehabilitative care after injury. These socioeconomic and racial/ethnic disparities are reduced among insured patients. Prior to the implementation of the Affordable Care Act (ACA), more than 20% of hospitalized trauma patients were uninsured, with this proportion being much higher among low income and racial/ethnic minority patients. Medicaid expansion through the ACA was implemented to increase health insurance coverage among low income adults. It has reduced the percentage of trauma patients who are uninsured. However, its effects nationally on the known socioeconomic and racial/ethnic disparities that exist in trauma care and outcomes remain unclear. Lack of insurance is not the only mechanism underlying these disparities as being uninsured is correlated with numerous factors that may independently affect trauma outcomes, such as poorer pre-injury health status, greater treatment delay, provider bias, and treatment at lower resourced hospitals. However, evidence for the direct impact of insurance coverage on disparities in trauma outcomes comes from populations with universal insurance coverage such as the elderly and military personnel, in whom these disparities are not seen. Further research is needed to understand the effect of ACA Medicaid expansion on racial/ethnic and socioeconomic disparities in trauma care and outcomes and elucidate the mechanisms by which this policy may have reduced these disparities. This project will utilize 2010-2017 State Inpatient and State Emergency Department Databases from 18 US states as well as data on hospital structural and financial characteristics to evaluate the effect of ACA Medicaid expansion on socioeconomic and racial/ethnic disparities in trauma care and outcomes among young adults hospitalized for injury. We aim to evaluate whether ACA Medicaid expansion has mitigated disparities in in- hospital mortality, transfer patterns, unplanned readmissions, and access to rehabilitative care after serious injury for Non-Hispanic black patients, Hispanic patients, and patients from low income communities. We also aim to determine what types of hospitals have experienced the largest improvements in outcomes among their minority and low socioeconomic status young adult trauma patients. This project will provide policy makers and healthcare providers with a clear picture of the impact of health insurance expansion to low income adults on racial/ethnic and socioeconomic disparities in trauma outcomes. With the federal government and states debating a variety of changes to Medicaid, this project will provide timely information on the potential effects of such policies on the hundreds of thousands of young adults seriously injured in the US each year.